brain abscess in seven cats due to a bite wound -

672 JFMS CLINICAL PRACTICE

Journal of Feline Medicine and Surgery (2011) 13, 672–680

C A S E S E R I E S

Clinical Practice

Bacterial infection of the central nervoussystem (CNS) may result in an abscess –that is, a localised collection of purulentmaterial within the CNS, its surroundingmembranes, or in the epidural space.1

Brain abscesses are uncommon in dogs andcats, and may arise as a result of various aeti-ological processes: spread from distant fociof infection (eg, bacterial endocarditis, lungabscesses); penetrating injury to thecalvarium (eg, bite wound, bullet); directextension of infection from nasal sinuses, earsand eyes, or from diseased maxillary toothroots; use of contaminated surgical instru-ments; or penetration of the calvarium andbrain substances by a foreign body(eg, plant material, sewing needle).2–7

Additionally, brain abscesses can be the resultof a compromised immune system.8

Bacterial CNS abscesses can be polymicro-bial and are more commonly associated withaerobic bacteria (eg, Streptococcus, Staphy-lococcus, Pasteurella and Nocardia species) thananaerobic bacteria (Bacteroides, Fusobacterium,Peptostreptococcus, Actinomyces and Eubac-terium species).3,9–11

This report describes seven cats with a brainabscess secondary to a bite injury diagnosedby magnetic resonance imaging (MRI) andmanaged with a combination of medical andsurgical treatment.

Clinical histories

Seven adult cats aged between 3 and 13 yearswere presented for evaluation of progressiveneurological signs ranging in duration from1–6 days prior to presentation.

Cat 1Case 1, a 3-year-old male entire domesticshorthair (DSH) cat, presented with a 1-dayhistory of circling, head pressing, disorienta-tion and a single focal seizure. Two days priorto the onset of neurological signs, the cat wasreported to be inappetent and a subcutaneousabscess was identified over the dorsal part ofthe head. At that time clindamycin (Antirobe;Pfizer) 15 mg/kg PO and ketoprofen(Ketofen; Fort Dodge) 2 mg/kg SC weregiven. Due to deterioration in the clinicalsigns on the day of the referral the cat was

Presentation and lesion localisation Seven adult domestic shorthair cats were presented with a1- to 6-day history of progressive neurological signs. A focal skin puncture and subcutaneous swellingover the dorsal part of the head were detected on physical examination. Neurological examination indicatedlesion(s) in the right forebrain in four cats, multifocal forebrain in one cat, left forebrain in one cat, andmultifocal forebrain and brainstem in the remaining cat. In all cats, magnetic resonance imaging revealeda space-occupying forebrain lesion causing a severe mass effect on adjacent brain parenchyma.Clinical approach and outcome All cats were managed with a combination of medical and surgicaltreatment. At surgery a small penetrating calvarial fracture was detected in all cats, and a tooth fragmentwas found within the content of the abscess in two cats. The combination of surgical intervention,intensive care and intravenous antimicrobials led to a return to normal neurological function in five cats.Practical relevance As this series of cases indicates, successful resolution of a brain abscess due toa bite injury depends on early recognition and combined used of antimicrobials and surgical intervention.A particular aim of surgery is to remove any skull and foreign body (tooth) fragments that may representa continuing focus of infection.

Brain abscess in seven catsdue to a bite wound: MRI findings,surgical management and outcome

Chiara CostanzoDVM PhD MRCVS1

Laurent S GarosiDVM DipECVN MRCVS2

Eric N GlassBS MS DVM DipACVIM

(neurology)3

Clare RusbridgeBVMS PhD DipECVN

MRCVS4

Catherine E StalinMA VetMB DipECVN4

Holger A VolkDVM PhD PGCA

DipECVN FHEA MRCVS5

1Department of VeterinaryClinical Sciences,

University of Teramo, Italy2Davies Veterinary

Specialists, Higham Gobion,Hertfordshire, UK

3Red Bank VeterinaryHospital, Tinton Falls,

New Jersey, USA4Stone Lion Veterinary

Hospital, London, UK5Department of Veterinary

Clinical Sciences,Royal Veterinary College,University of London, UK

Corresponding author:Chiara Costanzo,

[email protected]

Date accepted:14 March 2011

1098-612X/11/090672+09 $36.00/0© 2011 ISFM and AAFP. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.jfms.2011.07.020

JFMS CLINICAL PRACTICE 673

given a single dose of amoxicillin clavulanate(Augmentin; GlaxoSmithKline) 17 mg/kg IV,metronidazole (Metronidazole; BaxterHealthcare) 10 mg/kg IV, meloxicam(Metacam; Pfizer) 0.3 mg/kg SC, dexametha-sone (Dexadreson; Intervet) 1 mg/kg IV andintravenous isotonic sodium chloride infusionat maintenance rate.

On physical examination a focal skin punc-ture and a subcutaneous abscess on the rightfrontal part of the head were found.Neurological evaluation revealed an obtundedmental status, propulsive circling to the right,postural reaction deficits in all four limbs butmore severe on the left side, left-sided Horner’ssyndrome, and an absent menace response andabsent visual placing response with normalpupillary light reflex (PLR) in both eyes. Theseneurological findings suggested a predomi-nantly right-sided forebrain lesion.

Cat 2Case 2, a 7.5-year-old male neutered DSH cat,presented with a 6-day history of lethargy andanorexia; the cat’s condition had deterioratedin the past 24 h with the onset of bilateral thirdeyelid protrusion and disorientation. Prior toreferral, the cat was treated with a single doseof enrofloxacin (Baytril; Bayer HealthCare) 5mg/kg SC, buprenorphine (Vetergesic; Alstoe)0.02 mg/kg IM and intravenous Hartmann’sfluid (Baxter Healthcare) at twice maintenancerate. The owner reported that 2 weeks earlierthe cat had a fight which resulted in a woundon top of his head.

Physical examination revealed third eyelidprotrusion, most pronounced in the right eye,and a healed wound on the right dorsal partof the head. Neurological examination revealedan obtunded mental status, circling to the right,an absent menace response and decreasedvisual placing response on the left side, left-sided Horner’s syndrome and pain reaction onpalpation of the skull. These neurological find-ings suggested a right forebrain lesion.

Cat 3Case 3, a 5.5-year-old female neutered domes-tic longhair (DLH) cat, presented with a 1-dayhistory of lethargy and cluster seizures. Thecat was given a single dose of carprofen(Norocarp; Norbrook) 2 mg/kg SC andcefovecin sodium (Convenia; Pfizer) 8 mg/kgSC, prior to referral.

Physical examination revealed a subcuta-neous abscess over the dorsal part of the head.Neurological evaluation revealed an obtund-ed mental status, postural reaction deficits inthe right thoracic and pelvic limbs, and anabsent menace response with normal PLR inboth eyes, suggesting a predominantly left-sided forebrain lesion.

Cat 4Case 4, a 4-year-old male neutered DSH cat,presented with a 1-day history of seizure, headpressing, reluctance to move and pyrexia(39.4°C). The cat had been started on amoxi-cillin clavulanate (Synulox; Pfizer) 12.5 mg/kgPO q12h for 2 days prior to referral.

On admission, physical examinationrevealed a wound over the right dorsal part ofthe head. Neurological examination revealedan obtunded mental status, lateral recumbentposture, tetraparesis, delayed postural reac-tions in all four limbs, an absent menaceresponse in both eyes, and severe anisocoriawith a dilated and unresponsive right pupil.The neurological findings suggested a pre-dominantly right-sided forebrain lesion withpossible right-sided tentorial herniation sec-ondary to elevated intracranial pressure (ICP).

Cat 5Case 5, a 12.5-year-old neutered female DSHcat, presented for a small puncture wound onthe right frontal part of the head assumed tobe subsequent to a cat fight. At the time the catwas pyrexic (39.7oC) and was treated withcefovecin sodium (Convenia; Pfizer) 8 mg/kgSC and meloxicam (Metacam; Pfizer) 0.3mg/kg SC single dose. Six days later the catre-presented as an emergency following arapid onset of neurological signs.

Physical examination was unremarkable; thewound was already healed and body temper-ature was back to normal. Neurological exam-ination revealed an obtunded mental status,compulsive circling to the left, bilaterallyabsent menace response, slight anisocoria withdilated left pupil, and poor consensual PLR,photophobia and central blindness in the righteye. The lesion localisation was left forebrain.

Cat 6Case 6, a 10-year-old male DSH cat, presentedwith a 7-day history of depressed mental sta-tus, circling to the right and pacing aimlessly.The cat was initially treated by the owner withcephalexin (Ceporex; Teofarma) 15 mg/kg POq12h for 2 days, and after that was presentedto the referring veterinarian for an abscessover the dorsal part of the head. The abscesswas flushed and clindamycin (Antirobe;Pfizer) 20 mg/kg PO q24h and meloxicam(Metacam; Pfizer) 0.15 mg/kg SC q12h werestarted, but 12 h later the cat had deterioratedwith bilateral myosis, bilateral absent menaceresponse and circling to the right.Enrofloxacin (Baytril; Bayer HealthCare) 5mg/kg SC and prednisolone (Prednicare;Animalcare) 2 mg/kg PO q24h were startedfor 7 days, but clinical signs progressed withbilateral third eyelid protrusion, mydriasis, anabsent PLR and rectal temperature of 39°C.

CASE SER IES / Brain abscess due to bite wound in seven cats

Bacterial

CNS abscesses

can be

polymicrobial

and are more

commonly

associated

with aerobic

bacteria than

anaerobic

bacteria.



At the time of presentation the cat waspyrexic (41.1°C). Neurological examinationrevealed a severely obtunded mental status,upper motor neuron ambulatory tetraparesis,intermittent head pressing, right-sided cir-cling, abnormal postural reactions in all fourlimbs but worse on the left side, bilaterallyabsent menace response with intact PLR anddecreased physiological nystagmus in botheyes. The lesion localisation was multifocalforebrain and brainstem.

Cat 7Case 7, a 13-year-old male DSH cat, presentedwith a 2-day history of lethargy and swellingover the dorsal part of the head. Two monthsearlier the cat had undergone a left rostral ten-torial craniectomy for meningioma resection,from which he recovered uneventfully. Thecat was not on any medication at the time ofreferral.

Physical examination was unremarkableexcept for the presence of a wound and anabscess on the right dorsal part of the head.Neurological examinationrevealed an obtundedmental status, intermit-tent circling to theright, mild hemi-paresis anddelayed posturalreactions on theleft side, and anabsent menaceresponse in the lefteye. These signswere consistentwith a right forebrainlesion.

MRI examination and findings

All cats underwent MRI of the brain. Imageswere acquired on MRI units at differentcentres (1.5 T Gyroscan NT Intera, PhilipsMedical Systems, Surrey, UK [cats 1 and 2];Vet Esaote 0.2 Tesla permanent magnet,Esaote, Genoa, Italy 1.0 [cats 3, 4 and 5]; 0.4 TAperto MRI, Hitachi, Tokyo, Japan [cat 6];T Signa Horizon LS 1.0 GE Medical SystemsMilwaukee, WI [cat 7]).

As a minimum, T2-weighted images (WI) intwo planes (transverse and sagittal) wereobtained. Transverse T1WI, and transverseT1WI after intravenous IV paramagnetic con-trast medium (gadolinium) administration,were also obtained in all cases, with the excep-tion of one cat (cat 4) because of financialrestrictions. Transverse fluid attenuationinversion recovery (FLAIR) images were per-formed in two cases (cats 1 and 2). Additionalsequences were obtained as requested by theattending neurologist and radiologist. Allimages were interpreted by a board-certifiedveterinary radiologist and/or board-certifiedveterinary neurologist.

Cat 7 underwent repeat MRI of the brain2 weeks after surgery and 2 years later formeningioma regrowth. Cat 6 had another MRIstudy performed 7 weeks after surgery.

In all cats, MRI study revealed a predomi-nantly intra-axial space-occupying lesion inthe frontal or parietal region, diffuselyhypointense on T1WI, with a hyperintensecore and hypointense margins on T2WI,and strong ring enhancement. There weresevere secondary effects on adjacent brainparenchyma such as perilesional whitematter oedema with subfalcine (cats 1 and 2),

FIG 1 Magnetic resonance (MR) images fromcase 1 – T1WI before and after gadolinium(GAD) administration, T2WI and FLAIR. Theimages reveal an intra-axial space-occupyinglesion with well-defined margins in the rightfrontoparietal lobe, with an isointense core inFLAIR, hyperintense on T2WI and hypointenseon T1WI with marked ring enhancement.The perilesional oedema is moderate in thiscase. The muscles and subcutaneous tissueabove the brain lesion and the skull arehyperintense on T2WI and show diffusecontrast uptake on T1WI

Differential diagnosesconsidered

All cats had regular contact with othercats. Differentials considered based on the

results of neurological examination included aninflammatory/infectious CNS disease, primary ormetastatic brain tumour and, less likely, a cerebralbleed. In view of the presence of a focal skin punc-ture or subcutaneous swelling over the calvariumin all cats, an infectious process was consid-

ered the main differential.


subtentorial (cats 1, 2, 6 and 7) and foramenmagnum brain herniation (cat 7) (Figs 1 and 2).In all cats, a skull defect and ventrallydisplaced bone fragment was identifiedbetween the brain mass lesion and subcuta-neous tissue swelling detected on physicalexamination. This swelling appeared ashyperintensity on T2WI with contrastenhancement in the overlying temporalismuscle on T1WI (Fig 2). In cat 7, a skull defectwas observed at the level of the left parietallobe, which was the site of the previousdebulking meningioma surgery.

FIG 2 MR images from case 2 – tranverse T1WI before and after gadolinium administration, T2WI and FLAIR. The images reveal an intra-axial lesion in the rightfrontoparietal lobe, with an isointense core surrounded by hypointense margins on T1WI, hyperintense on T2WI and on FLAIR, with marked contrast enhancementon T1WI. The mass is surrounded by a diffuse perilesional oedema which contributes to the mass effect on the brain parenchyma, causing a subfalcine brainherniation and midline shift. The muscles and subcutaneous tissue over the visible skull lesion are hyperintense on T2WI and show diffuse contrast uptake on T1WI

Cat 1 Cat 2 Cat 3 Cat 4 Cat 5 Cat 6 Cat 7

Blood gasanalysis

Mg 0.57 mmol/l(RI 0.35–0.55);Glucose 7.47 mmol/l(RI 4.20–6.60);Hb 11.1 g/dl(RI 12.0–18.0);PCV 31%; TS 82

Mg 0.6 mmol/l(RI 0.35–0.55);Glucose 6.67 mmol/l(RI 4.20–6.60);PCV 37%; TS 80

Not performed Not performed pH 7.45(RI 7.24–7.40)

Urea 5.1 mmol/l(RI 5.36–12.14);Glucose 7.5mmol/l(RI 3.33–7.22)

Not performed

Haematology Unremarkableaccording to thereferring vet

Lymphopenia0.23 x 109/l(RI 1.5–7)

Not performed Within normallimits

RBC 3.9 x 1012/l(RI 5–10);HCT 28.5%(RI 30–45);PLT >100 x 103/µl(RI 175–600)

Not performed Lymphopenia1.3 x 103/mm3

(RI 1.8–6.5)

Biochemistry Unremarkableaccording to thereferring vet

Urea 5.9 mmol/l(RI 6.1–12);ALT 23 U/I(RI 25–130);CK 7738 U/I(RI 52–506)

Not performed Amyl 1796 U/l(RI 100–1200);Glucose14.59 mmol/l(RI 3.33–7.2);P 0.83 mg/dl(RI 2.4–8.2)

Within normallimits

Not performed Glucose274.5 mg/dl(RI 76–145);Lipase 2488 U/l(RI 100–1400)

Urinalysis Not performed SG 1030; pH 7;no growth on culture

Not performed Not performed Not performed Not performed Not performed

FIV/FeLV Not performed Negative Negative Negative Negative Not performed Negative

Coronavirus Not performed Not performed Not performed Not performed Not performed Not performed Negative

Toxoplasma Not performed Not performed Not performed Not performed Not performed Not performed IgG 1:256IgM negative

Swab fromabscess

Positive Positive Not performed Not performed Negative Negative Positive

Mg = magnesium, Hb = haemoglobin, PCV = packed cell volume, TS = total solids, RBC = red blood cells, HCT = haematocrit, PLT = plateletcount, ALT = alanine transaminase, CK = creatine kinase, P = phosphorus, Amyl = amylase, SG = specific gravity, RI = reference interval

TABLE 1 Diagnostic tests performed on seven cats with brain abscess secondary to a bite wound


Additional diagnostic tests

A complete blood count (CBC), serum biochem-ical analysis or blood gas analysis, urinalysis andinfectious disease serology were performed bythe referring veterinarian or on referral admis-sion (see Table 1, which lists predominantlyabnormal findings). Thoracic radiographs wereobtained in cats 2 and 7, and were normal.Abdominal ultrasound was performed in cat 2and revealed enlargement of the right kidneyand mesenteric lymph nodes, and one loop offluid-filled intestine, findings that were consid-



ered compatible with a mild nephropathy andenteropathy. Cerebrospinal fluid (CSF) collectionwas not attempted in any of the cats in view ofthe imaging findings suggestive of raised ICP.Swabs and fluid content collected from theintracranial abscess during surgery were sub-mitted for aerobic and anaerobic bacterial cul-ture in cats 1, 2, 5, 6 and 7, and were positive inthree cats. Pasteurella multocida and Escherichiacoli, sensitive to all antibiotics tested, includingpenicillin G, ampicillin, sulphadiazime/trimethoprim, clavulanic acid/amoxicillin, oxy-tetracycline, cephalexin, cefuroxime, cefovecinand enrofloxacin, were isolated in cases 7 and 1,

Route Days Cat 1 Days Cat 2 Days Cat 3 Days Cat 4 Days Cat 5 Days Cat 6 Days Cat 7

Clavulanic acidplus amoxicillin

IV 4 20 mg/kgq8h

10 20 mg/kgq8h

1 20 mg/kgq8h

5 17 mg/kgq8h

PO 30 12.5 mg/kgq12h

50 12.5 mg/kgq12h

28 20 mg/kgq12h

56 12.5 mg/kgq12h

SC 1 8 mg/kg q24h

Enrofloxacin IV 1 5 mg/kgq12h

2 5 mg/kg q12h

PO 56 5 mg/kg q12h

Marbofloxacin IV 5 2 mg/kg

SC 2 2 mg/kg

PO 4 2 mg/kg

Metronidazole IV 4 10 mg/kgq12h

10 10 mg/kgq12h

5 17 mg/kgq8h

1 10 mg/kgq12h

PO 16 10 mg/kgq12h

50 10 mg/kgq12h

28 15 mg/kgq12h

4 10 mg/kgq12h

Sulphadiazime/trimethoprim

SC 6 15 mg/kgq12h

PO 21 15 mg/kgq12h

Cephalosporin IV POp 22 mg/kg POp 22 mg/kg POp 22 mg/kg 1 30 mg/kg q6h 4 22 mg/kg q8h

IV 2 20 mg/kg q6h POp 22 mg/kg

SC 1 15 mg/kg q24h

PO 21 22 mg/kg q12h

Glucocorticoids IV 2 MPSS30 mg/kg

1 MPSS30 mg/kg

POp Dex 0.1mg/kg

POp+1

MPSS30 mg/kg

1 Dex0.2 mg/kg

1 Dex0.15 mg/kg

3 Dex 0.2mg/kg

PO 1048

Pred 1 mg/kgPred 0.5mg/kg

Furosemide IV 1 4 mg/kg DS 1 mg/kg

Mannitol IV POp 0.5 g/kg POp 1 g/kg POp 1g/kg twice POp 1 g/kg 1 1 g/kg stoppedafter 5 mins

POp 2 g/kg DS 1 g /kg

IV 2 0.5 g/kg 1 0.2 g/kg 1 1 g/kg

Phenobarbitone IV 2 2 mg/kgq12h

2 3 mg/kgq12h

POp 5.7 mg/kg 4 3 mg/kg

PO 180 3 mg/kgq12h

2 1.5 mg/kgq12h

Omeprazole IV 4 1 mg/kg

Ranitidine IV 1 2 mg/kg

Hospitalisation 5 Recovered 14 Recovered 1 Euthan 1 Euthan 10 Recovered 7 Recovered 9 Recovered

POp = perioperative, DS = during surgery, MPSS = methylprednisolone sodium succinate, Dex = dexamethasone, Pred = prednisolone, Euthan = euthanased

TABLE 2 Drug therapy, length of hospitalisation and outcome for seven cats with brain abscesssecondary to a bite wound

respectively; Corynebacterium species were isolat-ed in case 2, and found to be resistant toenrofloxacin and sulphadiazime/trimethoprimbut sensitive to all other tested antibiotics.

Cytology of the abscess fluid was performedin cat 1 and was consistent with a marked sep-tic suppurative inflammation. The vast majori-ty of the nucleated cells were neutrophils,which ranged from non-degenerate to marked-ly degenerate; lower numbers of macrophageswere present. A large mixed population ofbacteria was seen (rods, filamentous rods,cocci), often found in colony-like aggregatesand occasionally phagocytosed by neutrophils.



Outcome was determined based on at least one re-examination at the referralcentre in four cats (cases 2, 5, 6 and 7); follow-up of case 1 was obtained bymeans of owner telephone progress report 4 weeks after discharge. Two cats(cases 3 and 4), which required ventilatory support upon induction of anaesthe-sia, failed to regain consciousness and respiratory drive following surgery andwere euthanased at the owners’ request within 1 h of surgery.

Cats 1, 2, 5, 6 and 7 improved significantly and were discharged within 3–12days of surgery. At the time of discharge, neurological deficits were found,such as a unilateral reduced menace response in cats 5, 6 and 7, and ambula-tory tetraparesis and an absent menace response in cat 2; neurological exam-ination was normal in cat 1. Cats 2, 5, 6 and 7 were re-examined within 2–7weeks of surgery and found to be normal except for a slightly reduced menaceresponse in the left eye of cat 6.

Cat 6 had a repeat MRI examination 7 weeks after surgery that showed aCSF cavity at the site of the previously resected abscess and no contrastenhancement (Fig 4). Cat 7 underwent repeat MRI of the brain 14 days aftersurgery, revealing an ex vacuo dilatation of the right ventriculus, and meningealand superficial soft tissue contrast uptake at the site of the resected abscess.

FIG 3 Surgicaltreatment of cat 1.(a) Presurgicalappearance ofthe skin lesion.(b) Intraoperativeview of the skulldefect; purulentmaterial is arisingfrom the abscess.(c) Drainage andretrieval of pusfrom the brainabscess

FIG 4 MR images from case 6 before and 7 weeks after surgery – transverse T1WI beforeand after gadolinium (GAD) administration, and T2WI. The preoperative images reveal anintra-axial lesion in the right parietal lobe, hyperintense on T2WI and hypointense on T1WI,with strong ring enhancement after gadolinium administration. The right temporalis muscleand the subcutaneous tissue above the brain lesion are hyperintense on T2WI and T1WIand show contrast uptake. The perilesional oedema is severe in this case, with midlineshift. Post-surgery MRI scans of the brain reveal a CSF fluid cavity at the site of theprevious resected abscess, with no contrast enhancement or parenchymal oedema

a

b c

Treatment

All cats were managed with a combination ofmedical treatment, consisting of broad-spec-trum antibiotics, and surgery performed with-in 3 days of referral admission. Because ofrapid neurological deterioration and imagingevidence of suspected raised ICP, glucocorti-coids and mannitol were given in almost allcases. Perioperative drugs are listed in Table 2.

All cats were treated surgically via a rostro-tentorial craniectomy centered on the defect inthe parietal bone (Fig 3). At surgery, the fasciaand temporalis muscle appeared focally tornand necrotic and, below, a small penetratingfracture was detected in all cats. On comple-tion of the craniectomy, the underlying brainappeared swollen and a mucopurulent dis-charge was present immediately in the surgi-cal site. Swab and fluid content were taken foraerobic and anaerobic bacterial culture andsusceptibility testing in five cats (1, 2, 5, 6 and7). A large amount of purulent material wasdrained and a tooth fragment was foundwithin the content of the abscess in cats 4 and7. The surgical site was flushed with sterilesaline and abnormal brain tissue was debrid-ed. After extensive flushing the meningeswere left open to allow for drainage; in cat 3antibiotic was instilled (benzylpenicillin sodi-um, Crystapen; Genus Pharmaceuticals). Thehealthy fascia of the temporalis muscle wasreattached to its origin, the subcutaneousabscess was removed, and subcutaneoustissue and skin were closed. In one case (cat 1)a drain was left in place for 3 days.

O u t c o m e

of the capsule, which directly limits thespread of infection. In this late phase, thereis ongoing encapsulation and the necroticcentre continues to reduce in diameter.

In all seven cats, MRI revealed an intra-axialmass lesion that was diffusely hypointense onT1WI, with a hyperintense core andhypointense peripheral ring on T2WI. Thiswas causing a severe mass effect on adjacentbrain parenchyma with subfalcine, caudalsubtentorial and foramen magnum hernia-tion, as well as severe perilesional white mat-ter oedema (Figs 1, 2 and 4). Differentials con-sidered based on the results of both neurolog-ical examination and MRI included an infec-tious CNS disease and a primary or metastat-ic brain tumour. Meningiomas are the mostcommon brain tumour in cats and they have avaried appearance on T1WI and T2WI, usual-ly isointense and in some cases hypointenseon T1WI and hyperintense on T2WI; however,these tumours tend to show homogeneouscontrast enhancement and are extra-axial inlocation. Ring enhancement is often associat-ed with gliomas, but these neoplasms arisefrom an intra-axial location.

According to the reviewed literature,19–21 theMRI findings in our cases were suggestive ofan abscess in the late cerebritis phase (see box).

Therapeutic approachThe anatomic location, number and size ofabscesses, as well as the stage of abscess for-mation and neurological status of the patient,can influence the strategy for managing brainabscessation. Frequently a combination ofmedical and surgical treatment is required.



Discussion

This case series documents the occurrence ofbrain abscess subsequent to a bite wound inseven cats. All affected animals were present-ed several days after the injury with neurolog-ical signs consistent with a forebrain lesion; inone cat there were associated brainstem signsas well. In all cases a focal wound or a healedwound was observed on the dorsal part of thehead on physical examination, and two catswere pyrexic (39.4°C and 41.1°C).

In the reviewed literature there are only twoveterinary case reports of a successfully treat-ed brain abscess due to a bite wound, one in adog7 and one in a cat,12 and few reports inhumans,13–16 all of which have been treatedwith a combination of medical and surgicaltherapy; in a further report, a brain abscess ina cat due to a bite wound was diagnosed bypost-mortem examination.3 In human medi-cine, an intracranial pyogenic bacterial focus ofinfection remains a potentially fatal conditiondespite modern neurosurgical techniques,antibiotic treatment and the use of advancedimaging, such as computed tomography (CT)and MRI, allowing prompt diagnosis.

The successful management of brainabscesses depends on early recognition, thesite of entry, surgical treatment, optimalculture conditions and use of the appropriateantibiotic. With respect to pathogenesis, brainabscesses are almost always secondary to afocus of infection elsewhere in the body, andmay develop either after neurosurgery orbrain trauma.17 There is the additional possi-bility of infection resulting from bite woundsand migrating foreign body material.

Stages of abscess developmentBased on an animal model with CT scans,a series of stages of abscess development hasbeen described:18

� Days 1–3, ‘early cerebritis’ This stageis characterised by a necrotic central focus,oedema, and a surrounding zone ofperivascular inflammatory infiltratecomprising polymorphonuclear cells,lymphocytes and plasma cells.� Days 4–9, ‘late cerebritis’ The necroticzone becomes more discrete and issurrounded by a zone of hyperplasticfibroblasts and neovascularisation,extracellular oedema and hyperplasticastrocytes.� Days 10–14, ‘early capsule’ At this stagea distinct collagen capsule begins to appearwith a well developed layer of fibroblastsand an associated persistent cerebritis andneovascularity.� From day 14, ‘late capsule’ This stagecorresponds to the completion and thickening

In the first phase, a brain abscess appears to be hypointense on T1WI andhyperintense on T2WI and FLAIR images. In the late phase, ring enhance-ment may be present, and it is sometimes possible to observe a thin-walledrim of high signal (isointense to slightly hyperintense) on T1WI andhypointense on T2WI/FLAIR pre-contrast images; this is most likely due toparamagnetic free radicals secondary to the oxidative effect of the respira-tory burst of the bacteria and produced within macrophages during activephagocytosis at the abscess rim. Typically, a mature abscess appears onT1WI as a round and well-demarcated hypointense region with mass effectand peripheral low intensity oedema beyond the margins of the lesion. InT2WI and FLAIR images the necrotic material is hyperintense relative to theCSF and to the surrounding parenchyma of the brain. After gadoliniumadministration, the abscess always shows ring enhancement and, less com-monly, a multiloculated enhancement.

Brain abscesses may sometimes mimic necrotic tumours and cysticmetastases, but recent studies have shown that cerebral abscesses showrestricted diffusion on diffusion-weighted imaging (DWI).22

Neuroimaging studies have been the most useful diagnostic tools indetecting and localising early brain abscesses.17

M R I f e a t u r e s



A non-surgical approach is only possiblewhen the aetiological agent is known basedon positive cultures from CSF or fluid drainedfrom the abscess. In the present cases, CSF col-lection was not performed due to the risk ofbrain herniation associated with raised ICP.Furthermore, CSF evaluation may be of littlevalue in excluding an abscess from the differ-ential diagnosis list as cultures are often nega-tive in the face of bacterial infection of theCNS, and CSF analysis is rarely specific forbacterial abscesses.23,24

AntibioticsAll patients were started on broad-spectrumantibiotics while awaiting the results of cul-ture of swab material and fluid collected fromthe abscess during surgery. Positive cultureswere obtained in three out of four cats forP multocida, E coli and Corynebacterium species,reflecting the most common bacteria found ina cat’s mouth. In a study from Sweden whereoral swabs were collected from 38 cats thathad bitten humans, microbial culture yieldedPasturella species in 30 (79.9%) cats; 27 of the30 (90%) samples yielded P multocida (onesample yielded P haemolytica, and two micro-bial growths were not speciated). Additionalisolates included Prevotella oris-buccae andEnterobacter cloacae (from one sample each).Cultures of samples collected via gingivalscraping from a group of 25 control cats allyielded P multocida; a member of theEnterobacteriaceae family and viridiansgroup streptococci were detected in samplesfrom two and one control cat(s), respectively.25

Rational antimicrobial therapy in patientswith brain abscessation depends on selectingantibiotics that are able to penetrate theblood–brain barrier and into the abscesscavity and that have good activity against thesuspected pathogens. Ideally, intravenoustherapy is recommended for at least the first3–5 days of therapy; moreover in humans atleast a 6- to 8-week treatment course is war-ranted.17 The blood–brain barrier prevents thediffusion of many antibiotics in the CNS andthis represents a major limitation with regardto reaching therapeutic drug concentrations inthe CSF. High intravenous doses of ampicillinand third generation cephalosporins crossboth healthy and inflamed meninges extreme-ly well,26,27 enrofloxacin and metronidazoleare excellent antibiotics and trimethoprim-sulfonamide is bactericidal and readily pen-etrates the blood–brain barrier, even when it isnot inflamed.27

GlucocorticoidsFive of seven cats received glucocorticoids fora period ranging from 1–58 days. Althoughglucocorticoid use in the face of infection is

Successful

management of

brain abscess

depends

on early

recognition, the

site of entry,

surgical

treatment,

optimal culture

conditions

and use of the

appropriate

antibiotic.

usually contraindicated, in human medicinethere is abundant evidence that a transientanti-inflammatory dose of dexamethasone(0.15 mg/kg) q6h for 4 days can lead to lowerICP, lower inflammatory mediator concentra-tions, less CNS inflammation and generally asignificant improvement in outcome in peoplewith bacterial meningitis.28–30 Inflammatorymediators, such as tumour necrosis factor,prostaglandins, interferons and interleukin-1,are produced in response to bacteria and bac-terial cell wall lysis by the white blood cellsattracted to the infection focus as a result ofchemotaxis, and promote meningeal andependymal inflammation resulting in oede-ma, infarction and vasculitis.

Our patients were treated with several dif-ferent glucocorticoids. Three cats receivedmethylprednisolone sodium succinate on theassumption that a high dose protocol of thisdrug would provide benefit via free radicalscavenging action; however, a recent studyhas disputed this hypothesis.31 Based onevidence published in the human literature,dexamethasone may have been a more appro-priate choice in our cats.

MannitolIn addition, and in accordance with the litera-ture, all patients received mannitol at leastonce during surgery, in order to decrease ICP.Mannitol is considered the first-line therapyfor decreasing ICP, promoting the shift ofwater from the intracellular and interstitialspaces of the brain to the vasculature, induc-ing an osmotic diuresis and reducing cerebraloedema.32 Moreover, it has also been reportedto limit secondary oxidative injury in thebrain.33

SurgeryIn addition to intensive care and intravenousantimicrobials, all our patients underwentsurgical treatment consisting of a rostrotento-rial craniectomy, removal of the content of theabscess and extensive flushing of the surgicalsite before closing. In human medicine surgi-cal management of brain abscesses hasevolved recently with the development ofmini-invasive surgical techniques such asstereotactic aspiration of the abscess.Surgical intervention is considered the goldstandard treatment for brain abscess34 and, atthe same time, it allows collection of materialfrom within the abscess itself for definitivediagnosis and culture/sensitivity testing.Furthermore, in the current series of cases,surgical treatment enabled the removal ofskull fragments and foreign bodies, suchas the tooth fragments found in two cats,that may represent a continuing focus ofinfection.



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Conclusions

This is the first case series and, to our knowl-edge, only the third report of treatment ofbrain abscess due to a bite wound in compan-ion animals, and the second in cats. This series

indicates that successful management in suchcases depends on early recognition, andcombined used of antimicrobials and surgicalintervention in order to remove skull andforeign body (tooth) fragments that may rep-resent a continuing focus of infection.

brain abscess in seven cats due to a bite wound -

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